Horizontal injection molding machines mainly comprise a mold clamping apparatus for clamping a mold, and an injecting apparatus for injecting a resin material into the mold while the mold is clamped. In general, the mold clamping apparatus includes a fixed platen for supporting a fixed mold, a mold clamping cylinder disposed parallel to the fixed platen, tie bars extending between the mold clamping cylinder and the fixed platen, and a movable platen slidably guided by the tie bars and moved by the mold clamping cylinder, the movable platen supporting thereon a movable mold.
The clamping cylinder is configured to perform a movable mold displacing operation and a mold clamping operation in sequence. In recent years, however, in order to reduce the processing time and increase the productivity, improved arrangements have been proposed wherein the mold clamping cylinder performs only the mold clamping operation and another mold opening/closing actuator is provided for performing the movable mold displacement operation. One example of such improved arrangements is shown in Japanese Patent (JP-B) No. 3881764.
As shown in FIG. 1 of JP 3881764 B, a fixed platen (5) is fixed on a frame (1), a mold clamping cylinder (23) is disposed parallel to the fixed platen (5), tie bars (27, 27) extend between the mold clamping cylinder (23) and the fixed platen (5), and a movable platen (9) is arranged to be guided by the tie bars (27, 27). Note that reference signs in parentheses are those reference signs used in JP 3881764 B.
The movable platen (9) and the fixed platen (5) are connected by a mold opening/closing cylinder (17) such that the movable platen (9) is horizontally movable by the mold opening/closing cylinder (17). The mold clamping cylinder (23) is fixed a proper position on the tie bars (27) by means of half nuts (29).
The fixed mold (3) disposed on the fixed platen (5) and the movable mold (7) disposed on the movable platen (9) are mated together to form an injection space (mold cavity), and a molten resin material is injected into the injection space. After the injected resin material solidified, the mold opening/closing cylinder (17) is operated to move the movable platen (9) in a mold opening direction. Then, a molded article is removed from the mold and, thereafter, the mold opening/closing cylinder (17) is operated again to move the movable platen (9) in a mold closing direction until the movable mold (17) comes into contact with the fixed mold (3). Subsequently, the mold clamping cylinder (23) is operated to perform a mold clamping operation in preparation for injection of a molten resin material.
The frame (1) has a sliding plate (41) bonded thereto, and a base (45) is horizontally movably mounted on the sliding plate (41). The mold clamping cylinder (23) is fixed to the base (45). The mold clamping cylinder (23) and the movable platen (9) are mechanically connected together via a piston rod (26). With this arrangement, when the mold opening/closing cylinder (17) operates to move the movable platen (9), the base (45) moves on and along the sliding plate (41) in synchronism with movement with the movable platen (9). The sliding plate (41) is sufficiently long.
The base (45) has a relatively short sliding plate (43) bonded thereto, and the movable platen (9) is horizontally movably mounted on the sliding plate (43). The movable platen (9) is mounted on the base (45) which is largely movable and, therefore, the movable platen (9) moves relative to the sliding plate (43) over a short moving distance. This arrangement allows the sliding plate (43) to have a relatively small length.
A lubricating oil is applied to sliding portions formed between the sliding plate (41) and the base (45) and also between the sliding plate (43) and the movable platen (9) so that lubricity of the sliding portions is maintained. Since the base (45) moves on the sliding plate (41) over a relatively long distance, the lubricating oil is spread over the entire area of the sliding portion.
On the other hand, because the movable platen (9) moves on the sliding plate (43) over a relatively short distance, the lubricating oil is not spread sufficiently over the sliding portion and forms a part applied with the lubricating oil and another part devoid of the lubricating oil. As a consequence, lubricity of the sliding portion is deteriorated and seizure tends to occur. An arrangement, which is capable of increasing lubrication performance between the movable platen and the sliding plate, is therefore desired.
Although in JP 3881764B a related part of the description is omitted, the mold clamping apparatus shown in in JP 3881764 B requires a guide member provided to prevent displacement of the base (45) in a width direction of the frame (1) while the base (45) is moving on the sliding plate (41). Since the base (45) is movable over a relatively long distance, the guide member should be correspondingly long in length. The long guide member necessarily involves an increase in cost of the mold clamping apparatus. It is therefore desirable that the base (mold clamping cylinder) can be stably guided without requiring a separate guide member.